What is it about the Queen that inspires such deep affection in the British? As played by Helen Mirren in The Queen, HM was possessed of a steeliness, an impatience with cant and humbug and a sharp sense of humour. As portrayed by Alan Bennett in his quirky new novella, The Uncommon Reader, she is canny, intelligent and - most subversive of all - an increasingly avid reader who becomes convinced of the transformative power of literature.

Her discovery of books happens by chance: the corgis discover the City of Westminster mobile library parked outside the Buckingham Palace kitchens and the Queen, having calmed their yapping, feels duty-bound to borrow a book. Though Ivy Compton-Burnett proves a stodgy start, she ploughs on to the end and, appetite whetted, returns for another. Attracted by Nancy Mitford's The Pursuit of Love - 'Novels seldom came as well-connected as this and the Queen felt correspondingly reassured' - she begins a journey that encompasses autobiography, novels and non-fiction, taking in Proust, Henry James and Mary Renault, though not, unlike her mother, Dick Francis.

As her passion grows, so her entourage becomes increasingly alarmed, in particular her ambitious private secretary Sir Kevin Scatchard. 'I feel, ma'am, that while not exactly elitist, [reading] sends the wrong message. It tends to exclude.' None the less, she persists, drawn by the 'lofty indifference' of books: 'Books did not care who was reading them or whether one read them or not ... all readers were equal, herself included.'

Bennett's portrait of her is not only extremely funny, but also, one imagines, not far off the truth. Travelling by coach to state occasions, she becomes practised at waving and reading at the same time, 'the trick being to keep the book below the level of the window and to keep focused on it and not on the crowds'. As she works her way through the canon, her critical faculties become more acute. 'Am I alone,' she confides in her notebook, 'in wanting to give Henry James a good talking-to?' Through books, she discovers a way to express herself that has been denied her by her upbringing and vocation. Reading King Lear, she is moved by Cordelia's plight: 'Cordelia's "I cannot heave my heart into my mouth" is a sentiment I can readily endorse. Her plight is mine.'

The Uncommon Reader is a gloriously entertaining comic narrative, but it is also much more: a deadly serious manifesto for the potential of reading to change lives, for its ability to broaden horizons, to imagine oneself in others' shoes, and to enable one - or should that be One - to break out from the constraints of upbringing, class and education and lead the life you've always wanted. And, Bennett ponders, who might need that more than the Queen?

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